1. Field of the Invention
The present invention relates to materials, such as polymers, having barrier characteristics generally desirable in medical devices. More specifically, the barrier materials described herein are particularly suitable for medical products such as balloons associated with catheters, and sheaths for protectively covering the balloons.
2. Description of the Related Art
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. A catheter assembly having a balloon portion is introduced into the cardiovascular system of a patient via the brachial or femoral artery. The catheter assembly is advanced through the coronary vasculature until the balloon portion is positioned across the occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress the atherosclerotic plaque of the lesion against the inner wall of the artery to dilate the arterial lumen. The balloon is then deflated to a smaller profile to allow the catheter to be withdrawn from the patient's vasculature.
In treating the damaged vasculature tissue and to deter thrombosis and restenosis, therapeutic substances are commonly administered to the treatment site. For example, anticoagulants, antiplatelets and cytostatic agents are commonly used to prevent thrombosis of the coronary lumen, to inhibit development of restenosis, and to reduce post-angioplasty proliferation of the vascular tissue, respectively.
Systemic administration of such therapeutic substances in sufficient amounts to supply an efficacious concentration to the local treatment site often produces adverse or toxic side effects for the patient. Accordingly, local delivery is a preferred method of treatment since smaller total levels of medication are administered in comparison to systemic dosages, but the medication is concentrated at a specific treatment site. Local delivery thus produces fewer side effects and achieves more effective results.
A common technique for local delivery of therapeutic substances employs medicated stents. Stents that are capable of storing medication and releasing the medication at the implanted site are well known in the art. For example, a metallic stent is coated with a polymeric material which, in turn, is impregnated with a therapeutic substance or a combination of substances. Once the stent is implanted within a cardiovascular system lumen, the drug or drugs are released from the polymer for the treatment of the local tissues. U.S. Pat. No. 5,605,696 to Eury et al., U.S. Pat. No. 5,464,650 to Berg et al., and U.S. Pat. No. 5,700,286 to Tartaglia et al. are examples illustrating the use of a polymeric coating for the local delivery of a therapeutic substance or substances.
A problem associated with devices for carrying and delivering a therapeutic substance is diffusion of the substance from an element that carries the substance. Diffusion of the therapeutic substance from the carrying element potentially reduces the concentration and quantity of the substance below the level sufficient for effective treatment of the patient. In a catheter assembly, polymeric materials that contact the carrying element have a potential to significantly absorb the therapeutic substances. For example, drugs readily absorb into the wall layer of a balloon or a sheath of a catheter assembly that protects the balloon during packaging. Accordingly, it is desirable to prevent diffusion of drugs into other components of the catheter assembly, thereby preserving the concentration and quantity of the drugs carried by the catheter carrying element.